Fractures - General Principles

Fracture healing

Physiology of Fracture Healing

Fracture healing is a complex process that proceeds roughly through four overlapping phases (Fig. 20):

1. Haematoma formation (immediately after the fracture): At the time of fracture, damage to blood vessels occurs, leading to rapid haematoma formation at the fracture site. The haematoma activates inflammatory mediators (pro-inflammatory cytokines such as TNF-alpha, platelet-derived growth factors, and interleukins).
    
2. Granulation tissue & fibrocartilaginous callus (within 2 weeks): Fibrin-rich granulation tissue and angiogenesis at the fracture site are stimulated by activation of mesenchymal and inflammatory cells (such as fibroblasts and endothelial cells).
   Mesenchymal cells begin to differentiate, resulting in early chondrogenesis. Collagen-rich fibrocartilaginous callus forms at the fracture ends.
    
3. Formation of bony callus (from 2–3 weeks onwards): The fibrocartilaginous callus undergoes endochondral ossification. When the fracture fragments are not in direct contact, bridging callus develops: a hard, immature bony bridge that stabilises the bone fragments.
    
4. Bone remodelling (months to years): During bone remodelling, also referred to as consolidation, there is a continuous balance between bone resorption (by osteoclasts) and new bone formation (by osteoblasts), which eventually replaces disorganised bone with strong lamellar bone.